1. Field of the Invention
The invention relates to the field of magnetic bubble detectors, particularly those employing thin film members.
2. Prior Art
It is important in magnetic bubble devices to reliably detect the presence (or absence) of magnetic bubbles. One of the more common bubble detectors consists of an interconnected line of permalloy chevrons. This material also exhibits a change in resistance when propagating a magnetic bubble and this change is measured to detect the presence of a bubble. Typically, an active detector element and a "dummy" detector element are coupled in a bridge-like circuit; the dummy element nulls out the effects of the rotating, in-plane magnetic field on the active element.
In another case of bubble detectors, sometimes referred to as thin film detectors, a thin strip of magnetoresistive material (referred to sometimes hereinafter as a detection member) is insulated from and disposed beneath the propagation elements such as a line of chevrons. As a bubble is propagated by the line of chevrons, a change in resistance is sensed in the thin film member. (These members are typically 50-100 nm thick whereas the overlying permalloy elements are typically 500 nm thick.) Thin film elements have the advantage of providing an output signal which may be 4 times as large as the signal provided by a chevron detector. Obviously, thin film elements require additional processing for fabrication.
Thin film members are also coupled in a bridge-like configuration with a dummy member, again to null out the effects of the rotating, in-plane magnetic field. Such a detector is shown in FIG. 1 and will be discussed in more detail in conjunction with this figure.
The primary object of the present invention is to provide a reliable bubble detector. This is accomplished by providing a detector wherein the signal output from the detector is of a first polarity when no bubble is detected and of an opposite polarity when a bubble is present. This signal is easily matched to a sense amplifier. There have been numerous attempts in the prior art to match magnetic bubble detectors with sense amplifiers, or to otherwise provide matching between dummy detector members and active detector members. See, for example, U.S. Pat. Nos. 4,078,230; 4,146,867 and 4,035,785. Also see copending application Ser. No. 163,574 filed June 27, 1980 now U.S. Pat. No. 4,300,209 entitled "Method for Adjusting Signal Level Output From a Magnetic Bubble Detector", assigned to the assignee of the present application.